Pressure sensitive record sheets employing indole substituted pyromellitides



1910 CHAD-HAN LIN 3,540,914

PRESSURE SENSITIVE RECORD SHEETS EMPLOYING INDOLE SUBSTITUTEDPYROMELLITIDES Original Filed Jan. 30, 1967 FIG. I

BASE-SHEET OF RECORD MATERIAL COATED ON THE REAR WITH MINUTEPRESSURE-RUPTURABLE CAPSULES CONTAINING LIQUID SOLUTION OF CHROMOGENICMATERIAL DEVELOPABLE ON CONTACT WITH AN ELECTRON ACCEPTING MATERIAL OFTHE LEWIS- ACID TYPE TO COLORED FORM RECEIVING SURFACE OF UNDERSHEETCOATED WITH 2: DEL1E$;EONACCEPTING MATERIAL OF THE LEWIS- FIG. 2

nun-union;fi aggggggggggg INVENTOR CHAO-I-IAN LIN United States Patent3,540,914 PRESSURE SENSITIVE RECORD SHEETS EMPLOYING INDOLE SUBSTITUTEDPYROMELLITIDES Chao-Han Lin, Dayton, Ohio, assignor to The National CashRegister Company, Dayton, Ohio, a corporation of Maryland Originalapplication Jan. 30, 1967, Ser. No. 612,497, now Patent No. 3,491,117,dated Jan. 20, 1970. Divided and this application Jan. 24, 1969, Ser.No. 821,540

Int. Cl. B41m /22 US. Cl. 11736.2 29 Claims ABSTRACT OF THE DISCLOSUREPressure sensitive record unit and method of marking employingchromogenic material of normally colorless form having structuralformulae:

CIS CONFIGURATION 0 R1 R2 II 5 4 3 0/ 1y \0 TRANS CONFIGURATION where RR R and R consist of substituted and unsubstituted indolyl radicals anddialkylaminophenyl radi cals such that at least two indolyl radicals arepresent in a cis relationship in compounds having a cis configura tionand in a trans relationship in compounds having a trans configuration;said material assuming a colored form upon contact with a Lewis acidmolecule. Examples of these novel compounds include3,5-bis(p-diethylaminophenyl) 3 ,5 -bis( 1,2-dimethylindol-3-ylpyromellitide and 3 ,7-bis(1,2-dimethylindol-3 -yl) pyromellitide.

This is a division of application Ser. No. 612,479 filed Jan. 30, 1967,now US. Pat. No. 3,491,117.

This invention pertains to novel chromogenic compounds for use inpressure sensitive record material and to an improved mark-formingmanifold system incorporating these novel chromogenic compounds. Morespecifically, this invention pertains to indolyl derivatives ofpyromellitic acid which have the form of substantially colorless, i.e.white or slightly colored solids, or approach being colorless when inliquid solution, but which may be converted to dark-colored forms uponreactive contact with acidic material. As used in mark-forming systems,marking in desired areas on support webs or sheets may be accomplishedby eliecting localized reactive contact between the chromogenic materialand the acidic material on or in such a web or sheet, such materialbeing brought thereto by transfer, or originally there in situ, thedesired reactive contact forming dark-colored materials in the intendedimage areas.

Pressure-sensitive, mark-forming systems of the prior art include thatdisclosed in application for Letters Patent No. 392,404, filed Aug. 27,1964, by Robert E.

3,540,914 Patented Nov. 17, 1970 Miller and Paul S. Phillips, Jr., nowabandoned. The latter application provides a marking system of disposingon and/or within sheet support material the unreacted mark-formingcomponents (at least one of which is a polymeric material) and a liquidsolvent in which each of the mark-forming components is soluble, saidliquid solvent being present in such form that it is maintained isolatedby a pressure-rupturable barrier from at least one of the mark-formingcomponents until the application of pressure causes a breach or ruptureof the barrier in the area delineated by the pressure pattern. Themarkforming components thereby are brought into reactive contact,producing a distinctive mark.

It is an object of this invention to provide new and improved substanceshaving chromogenic properties which may be incorporated in a web orcoated onto the surface of a web to provide a novel manitolding unit,and which are useful in carrying out improved methods of markinginvolving reactive contact with a color-acti vating material to developdark-colored materials in areas where marking is desired.

It is another object of this invention to provide modified compounds,based upon the cis and trans-bis and tetrakis dimethylindolylpyromellitides, which are substantially colorless, or slightly colored,oliering a new and improved variety of chromogenic characteristics, anddeveloping novel dark-colored substances upon contact withcolor-activating materials.

It is a further object of this invention to provide a new and improvedmark-forming system which has the form of disposing within a web or uponthe surface of a web or sheet support material unreacted chromogenicmaterial which is capable of being reactively contacted with an acidicmaterial to produce a dark-colored substance, thus providing markshaving desirable color intensity and hue.

In accordance with this invention, there is provided a novelsubstantially colorless or slightly colored chromogenic compound havingthe structural formula:

CIS CONFIGURATION t w C C TRANS-CONFIGURATION where R R R and R consistof substituted and unsubstituted indolyl radicals and dialkylaminophenylradicals such that at least two indolyl radicals are present in a cisrelationship in compounds having a cis configuration and in a transrelationship in compounds having a trans configuration.

Examples of the novel compounds of this invention include:

cis-3,5-bis-(p-diethylaminophenyl) 3,5 bis(1,2-dimethylindol-3-yl)-pyromellitide having the structural formula:

Trans 3,7 bis (p-diethylaminophenyl)-3,7-bis-(1,2-dimethylindol-3-yl)-pyromellitide having the structural formula:

Trans 3,3,7,7 tetrakis (1,2 dimethylindol 3-yl)- pyromellitide Cis3,3,5,5 tetrakis (1,2-dimethylindol 3 yl)- pyromellitide O CHz-N N-CHaCH3 L CH:

U O n /5\ a 3 CHa O6\ /20 CHa 3 7 1 (3H 2 p CH3 In accordance withanother feature of this invention, a new composition of matter comprisesthe dark-colored substance having a resonant form developed by contactof a color-activating material with one of the above-mentionedchromogenic compounds. The color-developing or -activating material isan acidic substance for converting the chromogenic compound to theresonant form.

The method of marking of this invention, i.e., by desveloping adark-colored material from substantially colorless or slightly coloredchromogenic compounds comprises providing a chromogenic compoundselected from among the above-mentioned compounds and bringing suchchromogenic compound into reactive contact in areas where marketing isdesired with an acidic coloractivating substance to produce adark-colored resonant form of the chromogenic compound by the actionthereon in said areas of the said acidic substance.

The acidic materials employed in this invention can be any compoundwithin the definition of a Lewis acid, i.e., an electron acceptor.Preferably, acidic organic polymers such as phenolic polymers areemployed as the acidic material. The novel chromogenic materials exhibitthe advantage of improved color stability when reacted with suchphenolic polymers. The solution formation of the solid particles ofpolymeric material in the same solvent with the substantially colorlesschromogenic compounds allows penetration of the color into the supportsheet, if .porous, e.g., paper, so that the colored form of thechromogenic material sinks into the body of the sheet and is not merelyon the surface of the sheet. This feature protects against erasure ofrecorded data by attrition of the surface of the record sheet.

Reference is to be taken to the drawings. FIG. 1 is a diagrammaticrepresentation of a two-sheet unit manifold, a perspective in which thebottom surface of the overlying is supplied on the surface or near itwith a multiplicity of minute pressure-rupturable microcapsules, eachcontaining a droplet. Each droplet contains a solution of the basicchromogenic component. An acidic component, such as an acid clay or aphenolic polymeric material lies within the lower web or sheet or uponthe upper surface of the lower web or sheet. A colored mark is made bythe use of a stylus, a type character, or other pressurewriting meansapplied to the two-sheet unit manifold.

The encapsulated droplets are released on the rupture of the capsules inwriting operations, as shown in FIG. 2. The liquid of the releaseddroplets is transferred in the pattern of the data configuration to thetop of the underlying sheet. The top of the underlying sheet is coatedor impregnated with a material reactant with the chromogenie material,e.g., a phenolic polymer material having an acid-reacting OH group. Thedrawings show capsules on the over sheet containing a liquid solution ofchromogenic material. However, the capsules can contain the polymericphenolic material in liquid solution and the top surface of theunder-sheet may be supplied with the chromogenic material in particulateform. The improvement in the system is the chromogenic compound which isthe novel substance of the instant invention.

Referring again to FIG. 1 comprising an upper web or sheet having thechromogenic material dispersed with in or upon in a contiguousjuxtaposition, it is possible to incorporate the chromogenic material ina solid, crystalline-state in a binder material so that the chromogenicmaterial may be transferred from the upper web or sheet upon theapplication of pressure from a stylus to deposit some of the chromogenicmaterial on a surface carrying a color-activating polymeric material.Preferably, the chromogenic substance is dissolved in a solvent andminute droplets of the solution of the chromogenic material areencapsulated in minute, pressure-rupturable capsules. Obviously, manyother arrangements, configurations and relationships of the solvent andthe mark-forming materials, with respect to their encapsulation andlocation on the supporting sheet or webs can be envisioned. Sucharrangements are thoroughly described in the aforementioned applicationS.N. 392,404 to Miller et al., and need not be repeated herein.

It is noted that the polymeric mark-forming components should have acommon solubility with the chromogenic material in at least one liquidsolvent when the acid-reacting material is a phenolic or other organicacidic polymer.

It is also noted that in a single system several chromogenic materialsmay be used with the same or different polymeric materials. Severalpolymeric materials can be reactively contacted with a singlechromogenic compound or with a mixture of chromogenic compounds.

As mentioned above, the solvent is maintained in physical isolation inminute droplets until such time as it is released by application ofpressure. This may be accomplished by several known techniques, butpreferably isolation is maintained by individual encapsulation of thesolvent droplets in a microcapsule according to the proceduresdescribed, for example, in US. Pat. No. 2,712,507, issued to Barrett K.Green on July 5, 1955; 2,730,457, issued to Barrett K. Green and LowellSchleicher on Jan. 10, 1956; 2,800,457, issued to Barrett K. Green andLowell Schleicher on July 23, 1957; and 2,800,458, issued to Barrett K.Green on July 23, 1957, reissued as Reissue Pat. No. 24,899 on Nov. 29,1960. The microscopic capsules, when disposed within or upon asupporting web as a multiplicity in contiguous juxtaposition, arerupturable by pressure, such as normal marking pressures utilized, forexample, in writing or typing operating.

The material or materials chosen as the wall material of the microcapsule, in addition to being pressure rupturable, must be inert withrespect to the contents of the capsule and the other mark-formingcomponents so that the wall material remains intact under normal storageconditions until such time as it is released by the application ofmarking pressure. Examples of such wall materials are gelatin, gumarabic and many others thoroughly described in the aforementionedpatents.

For use in record material, the capsule size should not exceed 50microns in diameter. Preferably, the capsules should be smaller thanmicrons in diameter.

The acidic organic polymeric material useful in this invention includephenolic polymers, phenol acetylene polymers, maleic acid-rosin resins,partially or wholly hydrolyzed styrene-maleic anhydride copolymers andethylene-maleic anhydride copolymers, carboxy polymethylene and whollyor partially hydrolyzed vinyl methyl ether maleic anhydride copolymerand mixtures thereof;

Phenolic polymers found useful include alkylphenol acetylene resins,which are soluble in common organic solvents and possess permanentfusibility in the absence of being treated by cross-linking materials. Aspecific group of useful phenolic polymers are members of the typecommonly referred to as novolacs (as sold by Union Carbide Corp., NewYork, N.Y.), which are characterized by solubility in common organicsolvents and which are,

in the absence of cross-linking agents, permanently fusible. Generally,the phenolic polymer material found useful in practicing this inventionis characterized by the presence of free hydroxyl groups and the absenceof groups such as methylol, which tend to promote infusibility orcross-linking of the polymer, and by their solubility in organicsolvents and relative insolubility in aqueous media. Again, obviously,mixtures of acidic materials can be employed.

Resoles, if they are soluble, may be used, though subject to change inproperties upon aging.

A laboratory method useful in the selection of suitable phenolic resinsis the determination of the infra-red absorption pattern. It has beenfound that phenolic resins showing an absorption in the 3200-3500cmregion (which is indicative of the free hydroxyl groups) and nothaving an absorption in the 1600-1700 cm.- region are suitable. Thelatter absorption region is indicative of the desensitization of thehydroxyl groups and, consequently, makes such groups unavailable forreaction with the chromogenic materials.

The preparation of the phenolic formaldehyde polymeric materials forpracticing this invention is described in Industrial and EngineeringChemistry, volume 43, pages 134 to 141, January 1951, and a particularpoly- 6 mer thereof is described in Example 1 of US. Pat. No. 2,052,093,issued to Herbert Honel on Aug. 25, 1936, and the preparation of thephenol-acetylene polymers is described in Industrial and EngineeringChemistry, vol. 41, pages 73 to 77, January 1949.

The preparation of the maleic anhydride copolymers is described in theliterature, such as, for example, one of the maleic anhydride vinylcopolymers, as disclosed in the publication, Vinyl and Related Polymers,by Calvin E. Schildknecht, second printing, published April 1959, byJohn Wiley & Sons, Incorporated. See pages 65 to 68 (styrene-maleicanhydride copolymer), 628 to 630 (vinyl methyl ether-maleic anhydridecopolymer), and 530 to 531 (ethylene-maleic anhydride copolymer).

When the acidic material is one of the aforementioned organic polymers,the liquid solvent chosen must be capable of dissolving the mark-formingcomponents. The solvent may be volatile or non-volatile, and a single ormultiple component solvent may be used which is wholly or partiallyvolatile. Examples of volatile solvents useful in the afore-describedbasic chromogen-acidic polymer are toluene, petroleum distillate,perchloroethylene, and xylene. Examples of non-volatile solvents arehigh-boiling point petroleum fractions and chlorinated biphenyls.

Generally, the solvent chosen should be capable of dis solving at least0.3%, on a weight basis, of the chromogenic material, and about a 3-5%,on a weight basis, of the polymeric material to form an efficientreaction. However, in the preferred system, the solvent should becapable of dissolving an excess of the polymeric material, so as toprovide every oportunity for utilization of the chromogenic materialand, thus, to assure the maximum coloration at a reaction site.

A further criterion of the solvent is that it must not interfere withthe mark-forming reaction. In some instances, the presence of thesolvent may interfere with the mark-forming reaction or diminish theintensity of the mark, in which case the solvent chosen should besufficiently vaporizable to assure its removal from the reaction siteafter having, through solution, brought the markforming components intointimate admixture, so that the mark-forming contact proceeds.

Since the mark-forming reaction requires an intimate mixture of thecomponents to be brought about through solution of said components, oneor more of the markforming components may be dissolved in the isolatedsolvent droplets, the only requirement being that at least one of thecomponents essential to the mark-forming reaction be maintained isolateduntil reactively contacted with the other.

In the usual case, the mark-forming components are so chosen as toproduce a mark upon application of pressure at room temperature (20 to25 degrees contigrade). However, the present invention includes a systemin which the solvent component is not liquid at temperatures around roomtemperature but is liquid and in condition for forming solutions only atelevated temperatures.

The support member on which the components of the system are disposedmay comprise a single or dual sheet assembly. In the case where allcomponents are disposed on a single sheet, the record material isreferred to as a self-contained system. Where there must be a migrationof the solvent, with or without mark-forming component, from one sheetto another, the record material is referred to as a transfer system.(Such a system may also be referred to as a two-fold system, in that atleast two sheets are required and each sheet includes a component, orcomponents, essential to the mark-forming reaction.) Where a copiousamount of the colored reaction product in liquid form is produced on asurface of one sheet, it may produce a mark by transfer to a secondsheet as a colored mark.

In the preferred case, where microcapsules are employed, they may bepresent in the support material either disposed therethroughout or as acoating thereon,

or both. The capsules may be applied to the sheet material while stilldispersed in the liquid vehicle in which they were manufactured, or, ifdesired, separated and the separated capsules thereafter dispersed in asolution of the polymeric component (for instance, 30 grams of water and53 grams of a l aqueous solution of polyvinyl methyl ether maleicanhydride) to form a coating composition in which, because of theinertness of the solution and the capsules, both retain their identityand physical integrity. When this composition is disposed as a film onthe support material and dried, the capsules are held therein subject torupture to release the liquid contained. This latter technique, relyingon the inertness of the microcapsule and the dispersing medium of thefilm-forming mark-forming component, allows for a method of preparing asensitive record coating with the capsules interspersed directly in adry film of the polymeric material as it is laid down from the solution.A further alternative is to disperse in a liquid medium one or moremark-forming components, insoluble therein, and disperse in said mediumthe insoluble micfocapsules, with the result that all components of themark-forming system may be disposed on or within the support sheet inthe one operation. Obviously, the several components may be appliedindividually.

The respective amounts of the several components will vary, dependingprimarily upon the nature of the materials and the architecture of therecord material unit. Suitable lower amounts include, in the case of thechromogenic material, about .005 to .075 pound per ream (a ream in thisapplication meaning five hundred (500) sheets of 25" x 38" paper,totaling 3,300 square feet); in the case of the solvent, about 1 to 3pounds per ream; and in the case of the polymer, about /2 pound perream. In all instances, the upper limit is primarily a matter ofeconomic consideration.

In the instance where the mark-forming components are interspersedthroughout a single support sheet material (so-called self-containedunit), the following technique or procedure has been found useful:

The slurry of capsules may be applied to a wet web of paper as it existson the screen of a Fourdrinier paper machine, so as to sink into thepaper web a distance depending on the freeness of the pulp and the Watercontent of the web at the point of application.

The capsules may be placed directly in the paper or in a support sheet.Not only capsule structures, but films which hold a multitude ofdroplets for local release in an area subject to pressure are included.(See US. Pat. No. 2,299,694 which issued Oct. 20, 1942, to B. K. Green.)

With respect to the acidic organic polymeric component, a solutionthereof in an evaporable solvent is introduced into twice as much waterand agitated while the evaporable solvent is blown off by an air blast.This leaves an aqueous colloidal dispersion slurry of the polymericmaterial, which may be applied to the paper so as to leave a surfaceresidue, or the slurry may be applied to paper at the size-press stationof a paper-making machine by roller. In another method of making apolymersensitized sheet, the water-insoluble polymer is ground to thedesired particle size in a ball mill with water, preferably With adispersing agent, such as a small quantity of sodium silicate. If abinder material of hydrophilic properties is ground with the phenolicmaterial, the binder itself may act as a dispersant. If desired, anamount of binder material of up to 40%, by weight, of the employedamount of the polymeric material may be added to the ball-milled slurryof materials, such binder materials being of the paper coating binderclass, including gum arabic, casein, hydroxyethylcellulose, and latex(such as styrenebutadiene copolymer). If desired, oil absorbents in theform of fullers earths may be added to the polymeric material particlesto assist in retaining, in situ, the liquid droplets to be transferredto it in data-representing configuration, for the purpose of preventingbleeding of the print.

Another way of applying the chromogenic or polymeric materialindividually to a single sheet of paper is by immersing a sheet of paperin a 1% to 10% solution of the material in an evaporable solvent.Obviously, this must be done alone for each reactant, because if theother reactant material were present, it would result in a prematurecoloration over the sheet area. A dried sheet with one component thenmay be coated with a solution of the other component, the solvent ofwhich is a non-solvent to the already supplied component.

The polymeric material may be dissolved in ink composition vehicles toform a printing ink of colorless character and, thus, may be used tospot-print a proposed record sheet unit sensitized for recording in areactionproduced color in those areas by application of a solution ofthe chromogenic material.

In the case of phenolic polymer, a printing ink may be made of up to 75%weight, of the phenolic polymeric material in a petroleum solvent to aviscosity suitable for printing purposes. The relative amounts ofcomponents to be used are the most convenient and economical amountsconsistent with proper visibility of the recorded data. The resolutionof the recorded data is, among other things, dependent on particle size,distribution and amount of particles, liquid solvent migration, chemicalreaction elfciency, and other factors, all of which are things that maybe worked out empirically by one familiar with the art, and which do notdetermine the principle of the invention, which, in part, involves meansof enabling the bringing into solution, by marking pressure, of twonormally solid components in a common liquid solvent component heldisolated as liquid droplets, preferably in marking-pressure-rupturablecapsules having film walls, or else held isolated in a continuousmarking-pressurerupturable film as a discontinuous phase.

In the base-acid color system of this invention the acidic mark-formingcomponent(s) reacts with the basic chromogenic material(s) to effectdistinctive color formation or color change. In a multi-sheet system inwhich an acidic organic polymer is employed, it is desirable to includeother materials to supplement the reactants. For example, kaolin can beadded to improve the transfer of the liquid and/or the dissolvedmaterials between the sheets. In addition, other materials such asbentonite, attapulgite, talc, feldspar, halloysite, magnesiumtrisilicate, silica gel, pyrophyllite, zinc sulfate, zinc sulfide,calcium sulfate, calcium citrate, calcium phosphate, calcium fluoride,barium sulfate and tannic acid can be included.

Various methods known to the prior art and disclosed in theaforementioned application S.N. 392,404 to Miller et al. and UnitedStates patent application S.N. 420,193 to Phillips et al. can beemployed in coating compositions of the mark-forming materials intotheir supporting sheets. An example of the compositions which can becoated onto the surface of an underlying sheet of a twosheet system toreact with the capsule coating on the underside of an overlying sheet isas follows:

Coating composition: Percent by weight EXAMPLE I Preparation ofbis-(diethylaminophenyl) -(l,2-dimethylindol-3-yl) pyromellitide 9.0grams of N,N-diethylaniline, milliliters of benzene, and 5.5 grams ofpyromellitic dianhydride were stirred under ice-cooling. 16.0 grams ofaluminum chloride were slowly added. Stirring was continued for one hourunder ice-cooling, and at a temperature of 35 C. to 42 C. for two hours.A complex formed in the reaction vessel. 100 milliliters of 3 normalhydrochloric acid was added to decompose the complex. A solidprecipitated out of solution and a benzene layer formed in the reactionmixture; both were separated from the solution. The solution pH wasadjusted to 2.7 by the addition of ammonium hydroxide to precipitate ayellow solid exhibiting a weight of 6.9 grams. The crude product was amixture of two isomeric ketoacids having the following structures:

2.6 grams of the product prepared above, 1.45 grams of1,2-dimethylindole, and 20 milliliters of acetic anhydride were heatedin a 50 milliliter beaker on a hot plate. A solution was formed, but asolid precipitated out of solution after 5 minutes. The filtrate was setaside for use in the procedure delineated in Example II.

' The precipitate was dissolved in 120 milliliters of benzene and thenconcentrated to 25 milliliters whereupon a yellow solid exhibiting aweight of 0.4 gram precipitated out of solution. The solid was furtherpurified by repeatedly dissolving said solid in benzene, concentratingthe solution, and precipitation with petroleum ether to obtain one ofthe isomers of bis-(p-diethylaminophenyl)- bis-(1,2-dimethylindol-3-yl)pyromellitide exhibiting a melting point of above 300 C. A benzenesolution of the product turned blue when contacted with attapulgite claycoated on paper and a bluish green when contacted with a phenolicpolymer coated on paper.

EXAMPLE II Preparation of the second isomer of bis-(p-diethylaminophenyl) -bis- 1,2-dimethylindol-3-yl) pyromellitide Thefiltrate from the procedure of Example I and the washings of theprecipitate of Example I were combined and heated for minutes toslightly less than the boiling point of the solution. The filtrate wasthen poured into 100 milliliters of water, ammonium hydroxide was addedto adjust the alkalinity, and the mixture stirred for 30 minutes. Aprecipitate formed. The precipitate was sequentially purified byprecipitation from a benzene solution with petroleum ether to yield thesecond isomer of bis-(p-diethylaminophenyl) bis (1,2-dimethylindol-3-yl) pyromellitide which exhibited a melting point range of 255257 C. Abenzene solution of the product turned blue both when contacted withattapulgite clay coated on paper and with a phenolic polymer coated onpaper.

EXAMPLE III Preparation of tetrakis-(1,2-dimethylindol-3-yl)pyromellitide 3.2 grams of pyromellitic dianhydride, 5.0 grams of1,2-dimethylindole, and 40 milliliters of benzene were stirred underice-cooling. 4.4 grams of aluminum chloride was slowly added to thereaction mixture. After 10 minutes of stirring, the ice-bath wasreplaced with a water bath and the temperature of the water bath wasraised to 52 C. After an additional 30 minutes of stirring, 2.5milliliters of acetic anhydride was added. Stirring at 52 C. to 60 C.was continued for another 30 minutes time increment. 100 milliliters of3 normal hydrochloric acid was added and the reaction mixture washeated. A solid which had formed was collected, washed with water, andtreated with dilute ammonium hydroxide and filtered.

The solution was treated with activated charcoal, whereupon the solutionappeared to be a red color. Upon acidification of the red solution apurple solid exhibiting a weight of 2.6 grams precipitated out ofsolution. The crude product was a mxiture of two isomeric acids havingthe following structures:

CH3 CH3 1.0 gram of the purple solid, 0.8 gram of 1,2-dimethylindole,and acetic anhydride were heated for 20 minutes. The reaction mixturewas diluted with water and made alkaline with ammonium hydroxide,whereupon a solid product, one of the isomers oftetrakis-(1,2-dimethylindol 3-yl) pyromellitide, exhibiting a weight of1.4 grams precipitated out of solution. A benzene solution of theproduct turned purple when contacted with attapulgite clay coated onpaper and purple with a phenolic polymer coated on paper.

What we claim is:

1. A pressure sensitive record unit comprising:

:(a) support web or sheet material,

(b) mark-forming components and a pressure-releasable liquid solvent forsaid mark-forming components arranged in contiguous juxtaposition andsupported by said sheet material,

(c) said mark-forming components comprising at least one chromogeniccompound selected from the group consisting of:

and mixtures thereof, where R R R and R consist of 1,2-dialkylindol-3-yland p-dialkylaminophenyl, wherein alkyl has less than 5 carbon atomssuch that at least two indolyl radicals are present in a cisrelationship in compounds having a cis configuration and in a transrelationship in compounds having a trans configuration; and anelectron-accepting material of the Lewis acid type reactive with saidchromogenic material to produce a mark; which components uponpressure-release of the liquid solvent are brought into reactive contactin the released solvent.

2. The record unit of claim 1 wherein at least one of the mark-formingcomponents is maintained in isolation from the other mark-formingcomponents prior to the release of the solvent.

3. The record unit of claim 1 wherein the liquid solvent is present asthe nucleus of a microcapsule.

4. The record unit of claim 1 wherein the chromogenic material isdissolved in the isolated liquid solvent prior to pressure release.

5. The record unit of claim 1 wherein the mark-forming components andthe isolated liquid solvent are present in a single support sheet.

6. The record unit of claim 1 wherein at least one member selected fromthe group consisting of the mark-forming components and the liquidsolvent is present in a support sheet other than the support sheethaving the remaining members of the group.

7. The record sheet material of claim 1 where the electron-acceptingmaterial of the Lewis acid type comprises a clay.

8. The record sheet material of claim 1 where the electron-acceptingmaterial of the Lewis acid type comprises an organic'polymer.

9. The record sheet material of claim 1 where the electron-acceptingmaterial of the Lewis acid type comprises a phenolic polymer.

10. The record sheet material of claim 1 where the chromogenic compoundcomprises 3,5-bis-(p-diethylaminophenyl -.3 ,5 -bis- 1,2-dimethylindol-3-yl) pyromellitide.

11. The record sheet material of claim 1 where the chromogenic compoundcomprises 3,7-bis-(p-diethylaminophenyl 3,7-bis-(1,2-dimethylindoh3-yl)pyromellitide.

12. The record sheet material of claim 1 where the chromogenic compoundcomprises 3,3,7,7-tetrakis-(1,2-dimethylindol-3-yl) pyromellitide.

13. The record sheet material of claim 1 where the chromogenic compoundcomprises 3,3,5,5-tetrakis-(l,2- dimethylindol-3-yl) pyromellitide.

14. A mark-forming record sheet system comprising: A first web or sheethaving on one surface a transfer coating which contains as a finelydispersed phase a plurality of minute, pressure-rupturable, capsulescontaining as an inner phase a solvent vehicle; a second web or sheethaving an adherent coating upon its surface or dispersed within said webor sheet, said first and second webs or sheets being maintained disposedtogether in face-to-face relationship with said respective transfer andadherent coatings in contiguity with each other; a first coatingconstituent in the form of a substantially colorless or slightly coloredchromogenic material which includes a chromogenic compound selected fromthe group consisting of and mixtures thereof, where R R R and R consistof 1,2-dialkylindol-3-yl and p-dialkylaminophenyl, wherein alkyl hasless than 5 carbon atoms such that at least two indolyl radicals arepresent in a cis relationship in compounds having a cis configurationand in a trans relationship in compounds having a trans configuration;and a second constituent in the form of an electron-accepting materialof the Lewis acid type; one of said constituents being dissolved in saidsolvent liquid vehicle present as the inner phase of the plurality ofminute pressure-rupturable capsules in the transfer coating on or withinsaid first web or sheet, and the other of said coating constituentsbeing bonded to said second web in said adherent coating thereon butbeing accessible to other materials coming into contact with portions ofthe adherent coating, where by upon local impact and rupture of saidcapsules, releasing said liquid vehicle containing one coatingconstituent from at least some of the capsules onto said contiguousadherent coating, reactive contact is effected between said twoconstituents to produce a dark-colored material by the action of saidelectron-accepting material of the Lewis acid type upon said chromogenicmaterial to effect color change in said chromogenic compound to saidcolored form.

15. The mark-forming record sheet of claim 14 in which theelectron-accepting material of the Lewis acid type comprises a clay.

16. The mark-forming record sheet of claim 14 in which theelectron-accepting material of the Lewis acid type comprises an organicpolymer.

17. The mark-forming record sheet of claim 14 in which theelectron-accepting member of the Lewis acid type comprises a phenolicpolymer.

18. The mark-forming record sheet of claim 14 in which the chromogenicmaterial includes the compound 3,5- bis-(p-diethylaminophenyl)3,5-bis-(1,2-dimethylindol-3-yl) pyromellitide.

19. The mark-forming record sheet of claim 14 in which the chromogenicmaterial includes the compound 3,7-bis-(p-diethylaminophenyl) 3,7-bis(1,2-dimethylindol-3-yl) pyromellitide.

20. The mark-forming record sheet of claim 14 in which the chromogenicmaterial includes the compound 3,3,7,7-tetrakis-(1,2-dimethylindol-3-yl)pyromellitide.

21. The mark-forming record sheet of claim 14 in which the chromogenicmaterial includes the compound 3,3,5 ,5 -tetrakis-(1,2-dimethylindol-3-yl) pyromellitide.

22. The method of marking on a substrate by developing dark-coloredmaterials from chromogenic compounds comprising: providing as at leastone substituent a colorless or slightly colored chromogenic compoundselected from the group consisting of C l O O and mixtures thereof,where R R R and R consist of 1,2-dialkylindol-3-yl andp-dialkylaminophenyl, wherein alkyl has less than 5 carbon atoms suchthat at least two indolyl radicals are present in a cis relationship inthe compound having a cis configuration and in a trans relationship in acompound having a trans configuration; and bringing said chromogeniccompound into contact, in areas on said substrate sheet where marking isdesired, with an electron-accepting material of the Lewis acid type toproduce marks in said areas of a dark-colored material formed by theaction of said electron-accepting material on said chromogenic compound.

23. The method of claim 22 in which the electronaccepting material ofthe Lewis acid type is a clay.

24. The method of claim 22 in which the electronaccepting material ofthe Lewis acid type is an organic polymer.

25. The method of claim 22 in which the electron- References CitedIzigiepting material of the Lewis acid type is a phenolic UNITED STATESPATENTS ymer.

26. The method of claim 22 in which at least one chro- 2,505,486 1950mogenic compound is 3,5-bis-(p-diethylaminophenyl)-3,5- 5 3,244,549 4/1966 Farnham t a1. bis-(1,2-dimethylindol-3-yl) pyromellitide, 3,268,5378/ 966 G l at al- 27. The method of claim 22 in which at least one chro-3,336,337 1967 GQ ue mogenic compound is3,7-bis-(p-diethylaminophenyl)-3,7- 3,455,721 7/ 1969 h p etbis-(1,2-dimethylindol-3-yl) pyromellitide. 3,491,117 1/ 1970 L111- 28.The method of claim 22 in which at least one chro- 10 Y mogenic compoundis 3,3,7,7 tetrakis-(1,2-dimethylindol- MURRAY KATZ Pnmary Exammer 3-yl)pyromellitide.

29. The method of claim 22 in which at least one chromogenic compound is3,3,5,5-tetrakis-(1,2-dimethylindol- 117 -36.2, 36.8, 155 3-y1)pyromellitide. 15

